1. Field of the invention
The present invention relates to spiral drills with indexable inserts.
2. Discussion of related art
Spiral drills comprise a spiral part with cutting edges at a tip end, and a shank part which to at least some extent is bounded by cylindrical surfaces. With spiral drills for metal drilling it is of great importance that no chips are packed in the spiral flutes, since even a small counter pressure from adhering chips will seriously disturb the chip formation and lead to greatly increased feed and cutting forces, as well as slower feed rate.
To facilitate the chip flow through the spiral flutes these should be made with a spacious cross section shaped to avoid pressing the chips against the wall of the hole. It is also suitable to supply liquid through coolant channels to openings near the cutting edges, which facilitates chip formation and lowers friction in the flutes. In order not to lower the torsion stiffness or give an undesirable coupling between axial force and torsion angle, the drill can be made with two spiral coolant channels as shown in the patents SE 335 111 and DE 33 04 277, located between the flutes in the ribs where they are least detrimental to the strength and stiffness. Those patents show how a drill can be made from a such a spiral part joined to a separately made shank part with different location of coolant channels.
It is also known through patent SE 194 706 to make drills with indexable carbide inserts in pockets on a steel body, where it has been made possible to utilize a limited number of insert sizes for a large number of drill diameters by using two or more unsymmetrically located inserts, one of which is a center insert close to the center line of the drill and one of which is a peripheral insert close to the periphery of the drill.